Method of forming a local interconnect

ABSTRACT

A method of forming a local interconnect includes forming at least two transistor gates over a semiconductor substrate. A local interconnect layer is deposited to overlie at least one of the transistor gates and interconnect at least one source/drain region of one of the gates with semiconductor substrate material proximate another of the transistor gates. In one aspect, a conductivity enhancing impurity is implanted into the local interconnect layer in at least two implanting steps, with one of the implantings providing a peak implant location which is deeper into the layer than the other. Conductivity enhancing impurity is diffused from the local interconnect layer into semiconductor substrate material therebeneath. In one aspect, conductivity enhancing impurity is implanted through the local interconnect layer into semiconductor substrate material therebeneath.

RELATED PATENT DATA

This patent resulted from a divisional application of U.S. patentapplication Ser. No. 09/608,333, filed Jun. 29, 2000 now U.S. Pat. No.6,391,726, entitled “Integrated Circuitry, Methods of Fabricatingintegrated Circuitry, Methods of Forming Local Interconnects, andMethods of Forming Conductive Lines, naming H. Montgomery manning asinventor, the disclosure of which is incorporated by reference; whichpatent resulted from a divisional application of U.S. patent applicationSer. No. 09/266,456, filed Mar. 11, 1999, entitled “IntegratedCircuitry, Methods of Fabricating integrated Circuitry, Methods ofForming Local Interconnects, and Methods of Forming Conductive Lines,naming H. Montgomery manning as inventor, now U.S. Pat. No. 6,180,494,issued Jan. 30, 2001, the disclosure of which is incorporated byreference.

TECHNICAL FIELD

This invention relates to integrated circuitry, to methods offabricating integrated circuitry, to methods of forming localinterconnects, and to methods of forming conductive lines.

BACKGROUND OF THE INVENTION

The reduction in memory cell and other circuit size implemented in highdensity dynamic random access memories (DRAMs) and other circuitry is acontinuing goal in semiconductor fabrication. Implementing electriccircuits involves connecting isolated devices through specific electricpaths. When fabricating silicon and other semiconductive materials intointegrated circuits, conductive devices built into semiconductivesubstrates need to be isolated from one another. Such isolationtypically occurs in the form of either trench and refill field isolationregions or LOCOS grown field oxide.

Conductive lines, for example transistor gate lines, are formed overbulk semiconductor substrates. Some lines run globally over large areasof the semiconductor substrate. Others are much shorter and associatedwith very small portions of the integrated circuitry. This invention wasprincipally motivated in making processing and structure improvementsinvolving local interconnects, although the invention is not so limited.

SUMMARY OF THE INVENTION

The invention includes integrated circuitry, methods of fabricatingintegrated circuitry, methods of forming local interconnects, andmethods of forming conductive lines. In one implementation, a method offabricating integrated circuitry comprises forming a conductive linehaving opposing sidewalls over a semiconductor substrate. An insulatinglayer is deposited over the substrate and the line. The insulating layeris etched proximate the line along at least a portion of at least onesidewall of the line. After the etching, an insulating spacer forminglayer is deposited over the substrate and the line, and it isanisotropically etched to form an insulating sidewall spacer along saidportion of the at least one sidewall.

In one implementation, a method of forming a local interconnectcomprises forming at least two transistor gates over a semiconductorsubstrate. A local interconnect layer is deposited to overlie at leastone of the transistor gates and interconnect at least one source/drainregion of one of the gates with semiconductor substrate materialproximate another of the transistor gates. In one aspect, a conductivityenhancing impurity is implanted into the local interconnect layer in atleast two implanting steps, with one of the two implantings providing apeak implant location which is deeper into the layer than the other.Conductivity enhancing impurity is diffused from the local interconnectlayer into semiconductor substrate material therebeneath. In one aspect,a conductivity enhancing impurity is implanted through the localinterconnect layer into semiconductor substrate material therebeneath.

In one implementation, field isolation material regions and active arearegions are formed on a semiconductor substrate. A trench is etched intothe field isolation material into a desired line configuration. Aconductive material is deposited to at least partially fill the trenchand form a conductive line therein.

In one implementation, integrated circuitry comprises a semiconductorsubstrate comprising field isolation material regions and active arearegions. A conductive line is received within a trench formed within thefield isolation material.

Other implementations are disclosed, contemplated and claimed inaccordance with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor waferfragment at one processing step in accordance with the invention.

FIG. 2 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 3.

FIG. 5 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 4.

FIG. 6 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 5.

FIG. 7 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 6.

FIG. 8 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 7.

FIG. 9 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 8.

FIG. 10 is a diagrammatic sectional view of an alternate embodimentsemiconductor wafer fragment at one processing step in accordance withthe invention.

FIG. 11 is a view of the FIG. 10 wafer at a processing step subsequentto that shown by FIG. 10.

FIG. 12 is a view of FIG. 11 taken through line 12—12 in FIG. 11.

FIG. 13 is a view of the FIG. 10 wafer at a processing step subsequentto that shown by FIG. 11.

FIG. 14 is a view of FIG. 13 taken through line 14—14 in FIG. 13.

FIG. 15 is a view of the FIG. 10 wafer at a processing step subsequentto that shown by FIG. 13.

FIG. 16 is a view of FIG. 15 taken through line 16—16 in FIG. 15.

FIG. 17 is a diagrammatic sectional view of another alternate embodimentsemiconductor wafer fragment at one processing step in accordance withthe invention, and corresponds in sequence to that of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Referring to FIG. 1, a semiconductor wafer in process is indicatedgenerally with reference numeral 10. Such comprises a bulkmonocrystalline silicon substrate 12. In the context of this document,the term “semiconductor substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductor substrates describedabove.

A gate dielectric layer 14, such as silicon dioxide, is formed oversemiconductor substrate 12. A conductively doped semiconductive layer 16is formed over gate dielectric layer 14. Conductively doped polysiliconis one example. An insulative capping layer 18 is formed oversemiconductive layer 16. An example material is again silicon dioxide.Intervening conductive layers, such as refractory metal silicides, mightof course also be interposed between layers 16 and 18. An etch stoplayer 20 is formed over insulative capping layer 18. An examplepreferred material is polysilicon.

Referring to FIG. 2, the above-described layers over substrate 12 arepatterned and etched into a plurality of exemplary transistor gate lines22, 24 and 26. Lines 22, 24 and 26 have respective opposing sidewalls 27and 28, 29 and 30, and 31 and 32. Lines 22, 24 and 26 are shown in theform of field effect transistor gates, although other conductive linesare contemplated. LDD implant doping is preferably conducted to provideillustrated implant regions 33 for the transistors. One example implantdose for regions 33 would be 2×10¹³ ions/cm². Alternately, the LDDimplant doping can implanted after source/drain regions have been formed(or a combination of both). Forming LDD regions later in the processreduces the D_(t) seen by such implants.

Referring to FIG. 3, an insulating layer 34 is deposited over substrate12 and lines 22, 24 and 26. The thickness of layer 34 is preferablychosen to be greater than that of the combined etch stop layer, cappinglayer and semiconductor layer, and to be received between the transistorgate lines to fill the illustrated cross-sectional area extendingbetween adjacent gate lines. Example and preferred materials includeundoped silicon dioxide deposited by decomposition oftetraethylorthosilicate, and borophosphosilicate glass.

Referring to FIG. 4, insulative material layer 34 has been planarized.Such is preferably accomplished by chemical-mechanical polishing usingetch stop layer 20 of gates 22, 24 and 26 as an etch stop for suchpolishing.

Referring to FIG. 5, a layer of photoresist 36 has been deposited andpatterned. Insulative material 34 is etched to effectively form contactopenings 38, 39 and 40 therein to proximate substrate 12, and preferablyeffective to outwardly expose material of semiconductor substrate 12.For purposes of the continuing discussion, the exposed portions ofsemiconductor substrate 12 are designated as locations 42, 43 and 44.The depicted etching constitutes but one example of etching insulatinglayer 34 proximate lines 22 and 24 along at least a portion of facingsidewalls 28 and 29. Such portion preferably comprises a majority of thedepicted sidewalls, and as shown constitutes the entirety of saidsidewalls to semiconductor substrate 12.

With respect to line 26, the illustrated insulating layer 34 etching isconducted along at least a portion of each of opposing line sidewalls 31and 32. Further with respect to lines 22 and 24, such etching ofinsulating layer 34 is conducted along portions of sidewalls 28 and 29,and not along the respective opposing sidewalls 27 and 30. Further, suchinsulating layer 34 etching exposes conductive material of at least oneof the transistor gates, with such etching in the illustrated exampleexposing conductive material 16 of sidewalls 28, 29, 31 and 32 of theillustrated transistor gates. Further with respect to gate lines 22 and24, the insulative material is etched to remain/be received over the onesidewalls 27 and 30, and not sidewalls 28 and 29.

After etching of layer 34, at least one of the exposed sidewalls iscovered with insulating material. Such preferably comprises depositionof an insulating layer 46 over substrate 12; lines 22, 24 and 26; andplanarized and etched insulative material 34 to a thickness which lessthan completely fills at least some of the contact openings (FIG. 6).Such layer preferably comprises a spacer forming layer, with silicondioxide and silicon nitride being but two examples.

Referring to FIG. 7, spacer forming layer 46 is anisotropically etchedto form insulative sidewall spacers 47, 48, 49, 50 and 52. Suchconstitutes but one example of forming the illustrated insulativesidewall spacers. In one implementation, insulating layer 34 is receivedbetween at least one of the sidewalls and one of the sidewall spacers,for example as shown with respect to line 24 between sidewall 30 andspacer 49. Further with respect to this example line 24, insulativematerial 34 is received between the one sidewall 30 and the oneinsulative spacer 49 formed thereover, and is not received between theopposing sidewall 29 and the other spacer 48 formed thereover. Yet, inthe depicted section, insulative sidewall spacers 48 and 49, and 50 and52 are formed over each of the respective opposing line sidewalls oflines 24 and 26, wherein in the depicted section only one insulativespacer 47 is formed over one sidewall of line 22. Further, insulativematerial 34 received between sidewall 30 and insulative spacer 49 ofline 24 has a maximum lateral thickness which is greater than or equal(greater as shown) to a maximum lateral thickness of sidewall spacer 49.Source/drain implanting may occur at this point in the process, ifdesired.

Referring to FIG. 8, a local interconnect layer 56 is deposited tooverlie at least one of the transistor gates, and ultimatelyinterconnect locations 42, 43 and 44 of substrate 12, and is thusprovided in electrical connection therewith. An example preferredmaterial for layer 56 is polysilicon. Due to the spacing constraintsbetween the insulative spacers of lines 22 and 24 versus that of lines24 and 26, layer 56 completely fills contact opening area 38 and lessthan completely fills contact opening areas 39 and 40.

Depending on the circuitry being fabricated and the desires of theprocessor, layer 56 might be in situ conductively doped as depositedand/or separately implanted with conductivity enhancing impuritysubsequent to deposition. Further, any such subsequent implantings mightbe masked to only be provided within portions of layer 56 where, forexample, both n-type and p-type substrate regions are being conductivelyconnected by an ultimately conductive interconnect formed from layer 56.Most preferably, interconnect layer 56 will ultimately comprise suitablyconductively doped semiconductive material. Where such will compriseboth n-type and p-type doping material, another conductive strappinglayer, such as a refractory metal silicide, will ideally be formed atoplayer 56 to avoid or overcome an inherent parasitic diode that formswhere p-type and n-type materials join. Further with respect to combinedn-type and p-type processing, multiple local interconnect layers mightbe provided and patterned, and perhaps utilize intervening insulativelayers, spacers or etch stops. Further prior to deposition of layer 56,a conductive dopant diffusion barrier layer might also be provided.

Example preferred implantings, whether p-type, n-type, or a combinationof the same, is next described still with reference to FIG. 8. Suchdepicts two preferred implantings represented by peak implant locationsor depths 58 and 60. Such are preferably accomplished by two discreteimplantings which provide peak implant location 60 deeper relative tolayer 56 than implant 58. For example within layer 56 in contactopenings 38 and 39, regions of layer 56 are shown where peak implant 60is deeper within layer 56 than is peak implant 58. Yet, the peak implantlocation or depth for implant 60 is preferably not chosen to be so deepto be within conductively doped material 16 of lines 22, 24 and 26.Further in contact opening locations 39 and 40, the implanting toproduce depicted implant 60 is conducted through local interconnectlayer 56 and into semiconductor substrate material 12 therebeneath.Diffusing of the conductivity enhancing impurity provided within layer56 might ultimately occur from local interconnect layer 56 intosemiconductor substrate material 12 therebeneath within locations 42, 43and 44 to provide the majority of the conductivity enhancing impuritydoping for the source/drain regions of the illustrated transistor lines.Depending on the processor's desire and the degree of diffusion, suchsource/drain regions might principally reside within semiconductorsubstrate material 12, or reside as elevated source/drain regions withinlayer 56.

Further and as shown, layer 56 in certain locations acts as a spacer forthe deeper implant. Further, such may actually reduce junctioncapacitance by counter doping halo implants that are further away fromgate polysilicon. This can provide flexibility in the settings of thehalo implants.

Referring to FIG. 9, local interconnect layer 56 is formed (i.e., byphotopatterning and etching) into a local interconnect line 57 whichoverlies at least portions of illustrated conductive lines 22, 24 and26, and electrically interconnects substrate material locations 42, 43and 44.

Further considered aspects of the invention are next described withreference to FIGS. 10-16. FIG. 10 illustrates a semiconductor waferfragment 10 a comprising a bulk monocrystalline silicon substrate 12.Semiconductor substrate 12 has been patterned to form field isolationregion 64 and active area region 62. In the illustrated example,material 66 of field isolation region 64 comprises silicon dioxidefabricated by LOCOS processing. Such might constitute other material andother isolation techniques, for example trench and refill resulting frometching trenches into substrate 12 and depositing oxide such as by CVD,including PECVD.

Fragment 10 a in a preferred and exemplary embodiment comprises anextension of fragment 10 of the first described embodiment, such as anextension in FIG. 10 starting from the far right portion of FIG. 4 ofthe first described embodiment. Accordingly, insulating layer 34 isshown as having been deposited and planarized,

Referring to FIGS. 11 and 12, a trench 68 is etched into field isolationmaterial 66 and is received within insulating layer 34. Such includesopposing insulative sidewalls 77 and a base 79. Trench 68 in thisillustrated example extends to an edge 70 of isolation material 66proximate, and here extending to, active area substrate material 12 ofregion 62. An example preferred depth for trench opening 68 is 10% to20% greater than the combined thickness of the conductive and insulatingmaterials of gate stacks 22, 24 and 26.

Referring to FIGS. 13 and 14, a conductive material 72 is deposited toat least partially fill trench 68, and electrically connects withsubstrate material 12 of active area region 62. As shown, material 72 ispreferably deposited to overfill trench 68. The width of trench 68 ispreferably chosen to be more narrow than double the thickness of layerof material 72. Such preferred narrow nature of trench 68 facilitatescomplete filling thereof with conductive material 72 in spite of itsdepth potentially being greater than the globally deposited thickness oflayer 72.

Referring to FIGS. 15 and 16, conductive layer 72 has been etched toproduce the illustrated local interconnect line 75 which includes a linesegment 76 received within trench 68 over isolation material 66. A smalldegree of overetch preferably occurs as shown to assure complete removalmaterial 72 from over the outer surface of insulating layer 34. Ideally,the shape of trench 68 is chosen and utilized to define the entireoutline and shape of the conductive line being formed relative toisolation material 66. Further, conductive material of line 75preferably contacts material 66 of trench sidewalls 77 and base 79.

FIG. 17 illustrates an exemplary alternate wafer fragment 10 bembodiment corresponding to FIG. 16, but using a trench isolation oxide66 b as opposed to LOCOS oxide 66. An exemplary preferred trench filledline 68 b is shown.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A method of forming a local interconnectcomprising: forming at least two transistor gates over a semiconductorsubstrate; depositing a local interconnect layer to overlie at least oneof the transistor gates and interconnect at least one source/drainregion proximate one of the transistor gates with semiconductorsubstrate material proximate another of the transistor gates; implantingconductivity enhancing impurity into the local interconnect layer in atleast two implanting steps, one of the two implantings providing a peakimplant location in some portion of the layer which is deeper within thelayer than the other; and diffusing conductivity enhancing impurity fromthe local interconnect layer into semiconductor substrate materialtherebeneath.
 2. The method of claim 1 comprising conducting the oneimplanting relative to another portion of the local interconnect layerto have a peak implant location which is through said layer and withinthe semiconductor substrate material therebeneath.
 3. The method ofclaim 1 wherein the semiconductor substrate material comprises bulksubstrate material.
 4. The method of claim 1 wherein the semiconductorsubstrate material comprises bulk monocrystalline silicon.
 5. The methodof claim 1 wherein the one and other implants are of the sameconductivity type.
 6. The method of claim 1 wherein the one and otherimplants are of different conductivity type.
 7. The method of claim 1comprising conducting the one implanting relative to one portion of thelocal interconnect layer to have a peak implant location which isthrough said layer and within an insulative capping layer of at leastone of the transistor gates.
 8. The method of claim 1 comprisingconducting the one implanting relative to one portion of the localinterconnect layer to have a peak implant location which is through saidlayer and within an anisotropically etched insulative sidewall spacerreceived proximate at least one of the transistor gates.
 9. A method offorming a local interconnect comprising: forming at least two transistorgates over a semiconductor substrate; depositing a local interconnectlayer to overlie at least one of the transistor gates and interconnectat least one source/drain region of proximate one of the transistorgates with semiconductor substrate material proximate another of thetransistor gates; and implanting conductivity enhancing impurity throughthe local interconnect layer into semiconductor substrate materialtherebeneath.
 10. The method of claim 9 further comprising in anotherimplanting step separate from said implanting, implanting conductivityenhancing impurity to a peals concentration location which is within thelocal interconnect layer.
 11. The method of claim 9 wherein thesemiconductor substrate material comprises bulk substrate material. 12.The method of claim 9 wherein the semiconductor substrate materialcomprises bulk monocrystalline silicon.
 13. The method of claim 9 alsocomprising conducting the implanting relative to one portion of thelocal interconnect layer to have a peak implant location which isthrough said layer and within an insulative capping layer of at leastone of the transistor gates.
 14. The method of claim 9 also comprisingconducting the implanting relative to one portion of the localinterconnect layer to have a peak implant location which is through saidlayer and within an anisotropically etched insulative sidewall spacerreceived proximate at least one of the transistor gates.